Induction cooking appliances are more efficient, have greater temperature control precision and provide more uniform cooking than other conventional cooking appliances. In conventional cooktop systems, an electric or gas heat source is used to heat cookware in contact with the heat source. This type of cooking is inefficient because only the portion of the cookware in contact with the heat source is directly heated. The rest of the cookware is heated through conduction that causes non-uniform cooking throughout the cookware. Heating through conduction takes an extended period of time to reach a desired temperature.
In contrast, induction cooking systems use electromagnetism which turns cookware of the appropriate material into a heat source. A power supply provides a signal having a frequency to the induction coil. When the coil is activated a magnetic field is produced that induces a current on the bottom surface of the cookware. The induced current on the bottom surface then induces even smaller currents (Eddy currents) within the cookware thereby providing heat throughout the cookware.
FIG. 1 depicts a schematic of a typical quasi-resonant inverter 100 for use in an induction heating system. As illustrated, inverter 100 includes an induction heating coil 102 that receives power from an AC source 104 by way of a rectifier 106. Induction heating coil 102 can be controlled by operation of a switching element 108. Switching element 108 in turn is controlled by one or more control devices that provide control signals to switching element 108. For instance, the control signals can be determined based at least in part on one or more feedback signals or other control signals provided from a controller associated with inverter 100.
In general, switching element 108 corresponds to the active component of a quasi-resonant inverter, which can be controlled in a known manner by the one or more control devices to provide power to induction heating coil 102 and/or a load (not shown), such as any vessel (e.g. cooking utensil) or object located on a cooktop proximate induction heating coil 102, and/or magnetically coupled to induction heating coil 102.
Operation of inverter 100 (or similar quasi-resonant inverter) in an induction heating system may produce substantial thermal stresses on switching element 108 due at least in part to temperature rise in the switch junctions of switching element 108. Such thermal stress may prevent inverter 100 from operating switching element 108 at a high duty cycle, and thereby from transmitting a maximum (or near maximum) amount of available power to the load.